EP 0 976 919 B1 discloses an actuating device for bi-directionally adjusting a wastegate valve of a turbocharger of an internal combustion engine. The actuating device comprises an actuator drive for generating actuation forces and a coupling device for transmitting the actuation forces from the actuator drive to the actuator formed by the wastegate valve. To this end, the coupling device is drive-connected on one side to the actuator drive and on the other side to the actuator. The coupling device comprises at least a first coupling member, a second coupling member and a joint that connects the two coupling members to each other in an articulated manner. In the known actuation device, the joint is configured as a ball joint, which comprises a ball formed on the first coupling member and a cylindrical ball receptacle formed on the second coupling member, into which the ball is inserted axially. The actuator drive is configured in the known actuation device as a pneumatic drive, which drives the first coupling member linearly. The second coupling member is connected via a lever arrangement to the wastegate valve, which is mounted such that is can be displaced pivotably about a pivot axis. A linear adjustment movement of the actuator is thus converted into a rotary adjustment movement of the wastegate valve, that is, the actuator, inside the coupling device.
In such actuating devices, which couple kinematically different actuation movements with each other, for example a translatory movement with a rotary movement, at least one joint must be present inside the coupling device in order to avoid stresses inside the coupling device. The joint is designed such that it allows different inclination angles between the coupling members.
Other actuating devices that can likewise have such a construction can be used for example for adjusting a variable turbine geometry or for adjusting flaps of a fresh air system, for example control flaps, tumble flaps or swirl flaps.
The configuration of the joint as a ball joint can be problematic if comparatively large compressive forces must be transmitted but at the same time only comparatively little installation space is available. Reduced installation space limits the maximum ball diameter that can be used. The smaller the ball diameter, the larger the surface pressure and the smaller the compressive forces that can be transmitted.